Group 7 Flashcards
Describe the trend in reducing abilities of halide ions
Reducing ability increases down the group
Explain the trend in reducing abilities of halide ions
Reducing ability increases down the group
- Ionic size increases down the group
- Shielding increases
- Attraction between outer electron and nucleus decreases
- So electron is more easily lost
What is the type of reaction between halide and concentrated H2SO4
Acid base reaction
What is the general formula for the reaction between halide ion and concentrated H2SO4
H2SO4 + NaX —> NaHSO4 + HX
Ionic equation:
(H+ + X - —> HX)
What is the observation when Br2 is formed
Brown/orange fumes
What is the observation when I2 is formed
Black solid/ Purple fumes
What is the observation when SO2 is formed
Pungent gas
What is the observation when S is formed
Yellow solid
What is the observation when H2S is formed
Smell of bad eggs
Describe the trend in electronegativity of halides
Decreases down the group
Explain the trend in electronegativity of halides
Decreases down the group
- Atomic size increases
- Shielding increases
-Weaker attraction between nucleus and shared pair of e- of the covalent bond
State the trend in boiling point of the halides
Boiling point increases down the group
Explain the trend in boiling point of the halides
Boiling point increases down the group
- Molecular size increases
- Number of electrons increases
- Van der waals forces between molecules increases
- More energy required to overcome these forces
What is the best oxidising agent out of the halides
F2
What is the worst oxidising agent out of the halides
I2 (more shielding therefore worse at gaining an electron)
What is the best reducing agent out of the halide ions
I-
What is the worst reducing agent out of the halides
F-
What is observed when Cl2 is formed?
Green solution
What are the 4 main steps in testing for halide ions
1) Add HNO3
2) Add AgNO3
3) Add dilute NH3
4) Add concentrated NH3
Why do we add HNO3 (nitric acid) in the first step of identifying halide ions (why is silver nitrate acidified)
Write an equation for this reaction
Removes Co32- ions
(essential as Ag2CO3 is a white ppt)
2 HNO3 + Na2CO3 —> 2 NaNO3 + H2O + CO2
(Na is from compound like NaBr)
Which element is clearly identified after adding AgNO3 in the halide ion test
F-
(Gives a colourless solution)
(The others give white, cream and yellow)
Which element is clearly identified after adding DILUTE NH3 in the halide ion test. Write the equation for this reaction
Cl-
(In Cl- white ppt dissolves, Br- and I- have no visible change)
AgCl(s) + 2NH3(aq) —> [Ag(NH3)2]+(aq) + Cl- (aq)
Which element is clearly identified after adding CONCENTRATED NH3 in the halide ion test. Write the equation for this reaction
Br-
(In Br- cream ppt dissolves, I- has no visible change)
AgBr(s) + 2NH3(aq) —> [Ag(NH3)2]+ (aq) + Br - (aq)
What is the test for I- ions
No visible change after completing all 4 steps of halide ion test
What is the formula for the chlorate ion
ClO-
What is the equation for the reaction of chlorine and water without UV light, what type of reaction is this
Cl2 + H2O –>HCl + HClO (reversible)
Ionic:
Cl2 + H2O –> 2H+ + Cl- + ClO-
(Reversible)
Disproportionation reaction (Cl2 both oxidised and reduced)#
What is a disproportionation reaction?
One where the same species is both oxidised and reduced simultaneously
Why is the reaction of chlorine and water without UV a disproportionation reaction
Cl2 is both oxidised and reduced
Which species is oxidised and which species is reduced in the reaction of chlorine and water without UV
Cl2 is reduced and oxidised
What is the benefit of adding Cl2 to water
Cl2 kills microorganisms (useful in pools and drinking water)
What is the risk of adding cl2 to water
Cl is toxic to humans in large amounts
What is the equation for the reaction of Cl and water with UV (sunlight)
2Cl2 + 2H2O —> 4HCl + O2
Ionic:
2Cl2 + 2H2O —> 4H+ + 4Cl- + O2
(Green colour of Cl2 slowly fades as it reacts)
Which species is oxidised and which species is reduced in the reaction of chlorine and water with UV
2Cl2 is Reduced
2H2O is Oxidised
What is the chemical formula for bleach
Sodium Chlorate(I)
NaClO
What is the equation for the manufacture of bleach
What is the colour change for this reaction
Cl2 + 2NaOH –> NaCl + NaClO + H2O
Ionic:
Cl2 + 2OH- —> Cl- + ClO- + H2O
Pale green to colourless
Which species is oxidised and which is reduced in the reaction for the manufacture of bleach
Cl2 is oxidised and reduced
What type of reaction is the manufacture of bleach
Disproportionation
State the colours of precipitate formed when AgNO3 is added to Cl-,Br-, and I-
Write the ionic equation for each
Chloride (Cl-) ions: Produce a white precipitate of silver chloride
Ag+(aq) + Cl-(aq) –> AgCl(s)
Bromide (Br-) ions: Produce a cream precipitate of silver bromide
Ag+(aq) + Br-(aq) –> AgBr(s)
Iodide (I-) ions: Produce a yellow precipitate of silver iodide
Ag+(aq) + I-(aq) –> AgI(s)
Identify all the reduction products formed when solid sodium iodide reacts with concentrated sulphuric acid.
SO2
S
H2S
Write the 3 redox equations after the initial reaction between NaI and H2SO4
HI
The initial reaction is NaI (s) + H2SO4 (aq) → HI (g) + NaHSO4 (s)
I2
Concentrated sulfuric acid can oxidize HI to iodine (I2), which appears as a violet or purple vapor: 2HI (g) + H2SO4 (aq) → I2 (g) + SO2 (g) + 2H2O (l)
S
Concentrated sulfuric acid can oxidize HI to sulphur (S), which appears as a yellow solid: 6HI (g) + H2SO4 (aq) → 3I2 (g) + S (s) + 4H2O (l)
H2S
Concentrated sulfuric acid can oxidize HI to hydrogen sulphide (H2S), which has a strong odour of bad eggs: 8HI (g) + H2SO4 (aq) → 4I2 (g) + H2S (s) + 4H2O (l)
What is the half equation for so42- to SO3
SO42- + 4H+ + 4e- —> SO3 + 2H2O
What colour is F2, state a property of it
Very pale yellow gas
Highly reactive
What colour is Cl2, state a property of it
Greenish, reactive gas, poisonous in high concentrations
What colour is Br2, state a property of it
Brown-Orange liquid, gives off dense brown/orange poisonous fumes
What colour is I2, state a property of it
Shiny grey solid, sublimes to purple gas
What do more reactive halogens displace
Less reactive halide ions in a compound
Will a halogen displace a less reactive halide ion in solution if the halide is lower in the periodic table
Yes
What is the trend in oxidising ability of the halogens
Decreases down the group
What is observed when a solution of KCl is added to a solution of chlorine
Very pale green solution, no reaction
What is observed when a solution of KCl is added to a solution of bromine
Yellow-orange solution, no reaction
What is observed when a solution of KCl is added to a solution of iodine
Brown solution, no reaction
What colour is a test tube with chlorine present in solution
Very pale green solution (often colourless)
What colour is a test tube with bromine present in solution
Yellow - orange solution
What colour is a test tube with iodine present in solution
Brown solution (sometimes black solid present)
What is observed when a solution of KBr is added to a solution of chlorine
Write the ionic equation for this reaction
Yellow-orange solution, Cl has displaced Br
Cl2(aq) + 2Br –(aq) –> 2Cl –(aq) + Br2(aq)
What is observed when a solution of KBr is added to a solution of bromine
Yellow-orange solution, no reaction
What is observed when a solution of KBr is added to a solution of iodine
Brown solution, no reaction
What is observed when a solution of KI is added to a solution of chlorine
Write the ionic equation for this reaction
Brown solution, Cl has displaced I
Cl2(aq) + 2I–(aq) –> 2Cl –(aq) + I2(aq)
What is observed when a solution of KI is added to a solution of bromine
Write the ionic equation for this reaction
Brown Solution, Br has displaced I
Br2(aq) + 2I–(aq) —> 2Br–(aq) + I2(aq)
What is observed when a solution of KI is added to a solution of iodine
Brown Solution, no reaction
What does the colour of a test tube after a halogen displacement reaction tell us
The colour of the solution in the test tube shows which free halogen is present in solution. (NOT HALIDE ION)
Chlorine =very pale green solution (often colourless),
Bromine = yellow-orange solution
Iodine = brown solution
(sometimes black solid
present)
How do we make bleach
Reaction of chlorine with cold, dilute, aqueous NaOH
Why does the Cl2 we add to swimming pools have to be replaced regularly
Sunlight can decompose chlorinated water, yet no ClO- is made which is what kills bacteria
What are some uses of bleach
Cleaning products
Treating water
Which out of these is an oxidising agent and which is a reducing agent:
Halogen and halide ion
Halogen - Oxidising agent
Halide ion - reducing agent
Sketch the sable showing the products of the reaction between concentrated H2SO4 and Cl-, Br- and I-
NaF is the same as Cl
What is the product with the lowest oxidation state of S that H2SO4 can be reduced to when reacting with Cl- (furthest product it can be oxidised to)
NaHSO4
What is the product with the lowest oxidation state of S that H2SO4 can be reduced to when reacting with Br- (furthest product it can be oxidised to)
SO2
What is the product with the lowest oxidation state of S that H2SO4 can be reduced to when reacting with I- (furthest product it can be oxidised to)
H2S
What is the order of the possible products when halide ions react with concentrated H2SO4 in order from the highest oxidation state of S to the lowest
NaHSO4
SO2
S
H2S
What happens to halide ions when they react with concentrated H2SO4
They are oxidised to give a halogen
What is the observation when a hydrogen halide is produced
(HF, HCl, HBr, HI)
White steamy fumes evolved
What do we get when we add add concentrated NH3 to any silver halide apart from AgI
Tollens
Halide ion
